The iPad 2, the third- and fourth-generation iPad with Retina display and the iPad mini can be updated to iOS 7. The original iPad that rolled out in 2010 can not be updated.

iPod touch

Only the latest version of the iPod touch -- the fifth-generation models that rolled out last year -- can be updated to iOS 7.

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Fortunately for older devices, Apple is now reportedly letting those gadgets download the last version of apps that worked with whatever version of iOS they are running.

That is useful because over time as developers update their apps, they stop supporting previous versions of Apple's mobile software.

So if you have an iPhone running iOS 5 and you download an app such as Twitter, for example, Apple will offer "the last compatible version" of that app.

That doesn't mean older devices will be able to run apps forever -- sometimes other factors come into play that make older versions of apps unusable -- but it is a helpful new feature that should extend the life of Apple gadgets.